#region Copyright & License

//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#endregion

using System;
using System.IO;
using System.Text;

namespace log4net.DateFormatter {
  /// <summary>
  /// Formats a <see cref="DateTime"/> as <c>"HH:mm:ss,fff"</c>.
  /// </summary>
  /// <remarks>
  /// <para>
  /// Formats a <see cref="DateTime"/> in the format <c>"HH:mm:ss,fff"</c> for example, <c>"15:49:37,459"</c>.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public class AbsoluteTimeDateFormatter : IDateFormatter {
    #region Protected Instance Methods

    /// <summary>
    /// Renders the date into a string. Format is <c>"HH:mm:ss"</c>.
    /// </summary>
    /// <param name="dateToFormat">The date to render into a string.</param>
    /// <param name="buffer">The string builder to write to.</param>
    /// <remarks>
    /// <para>
    /// Subclasses should override this method to render the date
    /// into a string using a precision up to the second. This method
    /// will be called at most once per second and the result will be
    /// reused if it is needed again during the same second.
    /// </para>
    /// </remarks>
    protected virtual void FormatDateWithoutMillis(DateTime dateToFormat, StringBuilder buffer) {
      int hour = dateToFormat.Hour;
      if (hour < 10)
        buffer.Append('0');
      buffer.Append(hour);
      buffer.Append(':');

      int mins = dateToFormat.Minute;
      if (mins < 10)
        buffer.Append('0');
      buffer.Append(mins);
      buffer.Append(':');

      int secs = dateToFormat.Second;
      if (secs < 10)
        buffer.Append('0');
      buffer.Append(secs);
    }

    #endregion Protected Instance Methods

    #region Implementation of IDateFormatter

    /// <summary>
    /// Renders the date into a string. Format is "HH:mm:ss,fff".
    /// </summary>
    /// <param name="dateToFormat">The date to render into a string.</param>
    /// <param name="writer">The writer to write to.</param>
    /// <remarks>
    /// <para>
    /// Uses the <see cref="FormatDateWithoutMillis"/> method to generate the
    /// time string up to the seconds and then appends the current
    /// milliseconds. The results from <see cref="FormatDateWithoutMillis"/> are
    /// cached and <see cref="FormatDateWithoutMillis"/> is called at most once
    /// per second.
    /// </para>
    /// <para>
    /// Sub classes should override <see cref="FormatDateWithoutMillis"/>
    /// rather than <see cref="FormatDate"/>.
    /// </para>
    /// </remarks>
    public virtual void FormatDate(DateTime dateToFormat, TextWriter writer) {
      // Calculate the current time precise only to the second
      long currentTimeToTheSecond = (dateToFormat.Ticks - (dateToFormat.Ticks%TimeSpan.TicksPerSecond));

      // Compare this time with the stored last time
      // If we are in the same second then append
      // the previously calculated time string
      if (s_lastTimeToTheSecond != currentTimeToTheSecond) // lock so that only one thread can use the buffer and
        // update the s_lastTimeToTheSecond and s_lastTimeString

        // PERF: Try removing this lock and using a new StringBuilder each time
        lock (s_lastTimeBuf) {
          if (s_lastTimeToTheSecond != currentTimeToTheSecond) {
            // We are in a new second.
            s_lastTimeBuf.Length = 0;

            // Calculate the new string for this second
            FormatDateWithoutMillis(dateToFormat, s_lastTimeBuf);

            // Render the string buffer to a string
            string currentDateWithoutMillis = s_lastTimeBuf.ToString();

#if NET_1_1
  // Ensure that the above string is written into the variable NOW on all threads.
  // This is only required on multiprocessor machines with weak memeory models
						System.Threading.Thread.MemoryBarrier();
#endif
            // Store the time as a string (we only have to do this once per second)
            s_lastTimeString = currentDateWithoutMillis;
            s_lastTimeToTheSecond = currentTimeToTheSecond;
          }
        }
      writer.Write(s_lastTimeString);

      // Append the current millisecond info
      writer.Write(',');
      int millis = dateToFormat.Millisecond;
      if (millis < 100)
        writer.Write('0');
      if (millis < 10)
        writer.Write('0');
      writer.Write(millis);
    }

    #endregion Implementation of IDateFormatter

    #region Public Static Fields

    /// <summary>
    /// String constant used to specify AbsoluteTimeDateFormat in layouts. Current value is <b>ABSOLUTE</b>.
    /// </summary>
    public const string AbsoluteTimeDateFormat = "ABSOLUTE";

    /// <summary>
    /// String constant used to specify DateTimeDateFormat in layouts.  Current value is <b>DATE</b>.
    /// </summary>
    public const string DateAndTimeDateFormat = "DATE";

    /// <summary>
    /// String constant used to specify ISO8601DateFormat in layouts. Current value is <b>ISO8601</b>.
    /// </summary>
    public const string Iso8601TimeDateFormat = "ISO8601";

    #endregion Public Static Fields

    #region Private Static Fields

    /// <summary>
    /// Last stored time with precision up to the second, formatted
    /// as a string.
    /// </summary>
    static readonly StringBuilder s_lastTimeBuf = new StringBuilder();

    /// <summary>
    /// Last stored time with precision up to the second, formatted
    /// as a string.
    /// </summary>
    static string s_lastTimeString;

    /// <summary>
    /// Last stored time with precision up to the second.
    /// </summary>
    static long s_lastTimeToTheSecond;

    #endregion Private Static Fields
  }
}